This invention relates generally to detection systems and more particularly to a double feed detection system for printing and packaging machinery.
It is frequently necessary to determine if more than one sheet of substrate is being fed at one time to processing equipment in the printing and packaging industries since feeding of more than one sheet of the substrate to the processing equipment at the same time can result in equipment damage. In the past, detection systems to detect whether multiple sheets of substrate are being fed to printing or packaging machinery typically relied on a direct contact mechanism such as a roller which was in turn connected through appropriate linkages to a disabling device which disabled the downstream machinery for printing or processing the substrate. Thus, the machinery was stopped when more than one sheet of substrate was being fed so that the additional sheet could be removed before being fed through the machinery to prevent damage thereto. While this type of detector works reasonably well on relatively thick substrates, it is very difficult to get the necessary accuracy for use on thin substrates. Further, the mechanical linkages of the prior art type detectors become worn during use and drastically affect the detection accuracy of the device.